Clean, efficient, durable, safe, and affordable stoves are – along with clean fuels and other products like chimneys and heat retention cookers –central to most solutions to the health, environmental, and other risks inherent in cooking with fire. Cooking with clean fuels is the most common way to achieve the dramatic health and climate benefits that the Alliance seeks. Where solid biomass must be used, advanced clean cookstoves are most likely to achieve significant health and climate benefits. Processing the biomass into pellets or briquettes often facilitates advanced performance. Other stoves achieve important, but more modest progress and therefore may best thought of as intermediate or transitional solutions as the market for more advanced solutions is developed. The Alliance is working to promote internationally recognized standards and testing protocols that can measure how clean, efficient, and safe a given cookstove is. Below are examples of common types of cookstove technologies:
Advanced Biomass Cookstoves
There are two primary types of advanced biomass stoves that can achieve high levels of performance, forced air stoves and gasifier stoves, both of which can run on processed or raw biomass.
Forced air stoves have a fan powered, for example, by a battery, an external source of electricity, or a thermoelectric device that captures heat from the stove and converts it to electricity. This fan blows high velocity, low volume jets of air into the combustion chamber, which when optimized results in much more complete combustion of the fuel. In some cases these stoves appear to be more robust to variations in how users cook, as well.
Gasifier stoves force the gases and smoke that result from incomplete combustion of fuels such as biomass back into the cookstove's flame, where the heat of the flame then continues to combust the particles in the smoke until almost complete combustion has occurred, resulting in very few if any emissions. Typical gasifier stoves are known as Top Lit Updraft (TLUD) stoves because some fuel is lit on top of the stove, forcing combustible products to pass through the flame front before being emitted into the air.In a gasifier stove with a fan, the jets of air create superior mixing of flame, gas, and smoke and can be extremely clean. However, testing needs to confirm how robust these stoves are in field conditions.
Fuel Type: Raw or processed biomass
Health Impacts: Lab tests of advanced biomass and gasifier stoves on the market today indicate the potential to, and by as much as 98% for the better performing stoves. New advanced stoves under development today should be able improve on this potential, though substantial questions remain as to the replicability of these figures in actual operating conditions. Advanced stoves that are optimized for and fueled by a processed (uniform) fuel will very likely have much better results in field conditions.
Climate Impacts: Lab tests of advanced biomass stoves for climate forcing emissions found that fan stoves reduced net warming impact by nearly 60 percent and gasifier stoves by about 40 percent, when CO2 was considered. If the biomass was considered to be harvested sustainably, fan stoves reduced overall warming impact by about 95 percent while gasifier stoves reduced warming impact by about two-thirds. These analyses took into account both greenhouse gases and aerosols such as black carbon.
Efficiency: Lab testing of forced air fan stoves demonstrates reduced fuel use (relative to a 3-stone fire) ranging from 37 to 63 percent. Gasifier stoves save on fuel use, though generally less than fan stoves.
Alcohol cookstoves are pressurized or non-pressurized and can burn ethanol in liquid or in gelled or waxy forms. Most alcohol stoves can successfully combust ethanol in a fuel-water ratio of 80% and above, but some stoves endeavor to burn ethanol with higher water levels. Alcohol stoves do not require anhydrous ethanol (with the water removed), which is typically what is required for gasoline blending.
Fuel Type: Ethanol or methanol
Health Impacts: Ethanol and methanol burn very cleanly. Studies conducted in a number of countries, both in the laboratory and in household field tests, have shown the benefit of alcohol stoves in dramatically reducing indoor air pollution as compared to wood, charcoal and kerosene stoves. Alcohol stoves tend to produce significantly less CO (carbon monoxide) than stoves using kerosene or solid fuels and alcohol stoves that incorporate adequate oxygen in the combustion process achieve extremely low levels of CO.
Climate Impacts: Greenhouse gases released in the production and consumption of ethanol fuel are reabsorbed during the growth cycle of the plant material used to make the fuel. Especially damaging greenhouse gases like carbon monoxide and VOCs (volatile organic compounds) are not produced or produced only at extremely low levels. Black carbon aerosols, a potentially potent climate forcer, are essentially not produced by the combustion of ethanol and methanol.
Efficiency: Alcohol stoves function in a range of efficiencies with gelfuel stoves generally less efficient than liquid fuel stoves. The most efficient ethanol stoves are more efficient than solid fuel stoves and kerosene wick stoves and generally comparable to LPG and pressurized kerosene stoves.
Domestic biogas plants convert animal manure and human waste at the household level into combustible methane gas. This biogas can be effectively used in simple gas stoves for cooking.
Fuel Type: Biogas
Health Impacts: Biogas technology yields tangible health effects with regards to smoke reduction in the kitchen. Individual studies have found that biogas plant installation can significantly reduce respiratory diseases, including decreases in respiratory illness, eye infection, asthma and lung problems.
Climate Impacts: Unlike fossil fuel combustion, biogas production from biomass is considered CO2 neutral and therefore does not emit additional greenhouse gases (GHG) into the atmosphere. Several biogas programmes in Asia have managed to generate carbon revenues through the compliance and/or voluntary market.
Efficiency: The efficiency of a biogas cookstove ranges from 50 to 65 percent, depending on the gas pressure and the stove design.
Electric stoves convert electrical energy into heat for cooking. Use of electric stoves is limited to areas that have access to electricity, which often excludes rural communities. While these stoves are commonplace in the developed world, they are less so in developing countries where access to and cost of electricity limits their uptake.
Fuel Type: Electricity generated by any number of fuels (coal, oil, gas, nuclear, hydropower, solar, wind)
Health Impacts: Electric stoves are smokeless at the point of use and do not produce any emissions within a household, though electricity generation does contribute emissions that impact ambient air quality.
Climate Impacts: Electricity generation can (depending upon the fuel used to spin the turbines) contribute to greenhouse gas emissions and have negative impacts on the climate.
Efficiency: Electric cookstoves are considerably more fuel efficient than traditional open fires or crude cookstoves
Liquefied Petroleum Gas (LPG) Cookstoves
Liquefied petroleum gas (LPG) from a canister can be burned very cleanly for cooking. While there is increasing access to this clean burning fuel type in the developing world, primarily in urban areas, the cost barriers to using it – cost of a stove, the ongoing fuel, and the deposit for the gas canister – are substantial for low-income families.
Fuel Type: Liquefied Petroleum Gas (LPG)
Health Impacts: Lab testing confirms that cooking with propane or liquid petroleum gas (LPG) is vastly cleaner than cooking over an open fire – reducing emissions of most key pollutants by over 95%, and reducing energy use by about 50 to 70%. LPG improves both indoor and outdoor air quality by substantially reducing pollutants that are hazardous to health, such as SOx, NOx and particulate matter.
Climate Impacts: LPG is very clean burning and has lower greenhouse gas emissions than any other fossil fuel when measured on a total fuel cycle. However, LPG is a fossil fuel, and thus has a substantial carbon footprint. It has been estimated that the carbon impact of LPG per unit of energy delivered is substantially less than the net warming impact from other forms of solid biomass burned in a cookstove and produced fewer harmful emissions than other fuels such as petrol, kerosene, oil, and diesel.
Efficiency: Cooking with LPG is cost-effective, since a high proportion of its energy content is converted into heat. LPG can be up to five times more efficient than traditional fuels, resulting in less energy wasted and less household income spent on fuel for those families currently buying solid fuels for cooking. Lab testing results show that cooking with LPG reduces the weighed fuel to cook by nearly 90%, relative to cooking on an open fire.
Plancha (griddle) stoves are specialized stoves designed for areas of the world where common cooking practices include making tortillas (in the case of Mexico and Central America) or other meals that require a hot flat surface to prepare. The plancha stove is designed to enclose the fire and to exhaust the particulate matter and toxic vapors from combustion outside of the households via chimneys. Designs vary from built in place to modular stoves that are prefabricated and easy to install. The fuel utilized also can be diverse, ranging from different types of biomass (agricultural waste including corn stalks and dung; natural debris such as twigs, limbs and pinecones; and firewood) to charcoal.
Fuel Type: Biomass or charcoal
Health Impacts: As the plancha stove encloses the fire and emissions from combustion are exhausted from households, the positive health impacts are significant. Burn injuries are greatly reduced and the health issues associated with smoke (respiratory illness, cataracts, low birth weight) are potentially reduced depending on if the stove is well sealed and consequently does not permit emissions to leak inside the home. In some cases, the emissions reductions are up to 99.9% as compared to an open fire. Due to fuel use reduction (from 50 to 70%), other health problems are reduced (hernias, back and/or neck pain).
Climate Impacts: Lab tests conducted on plancha stoves demonstrate that indoor air emissions are reduced due to the chimney, but they are channeled to the outside, thus still impacting the climate. Combustion chamber designs that efficiently burn the fuel help to reduce outdoor emissions by 30% or more as compared to open fires, as long as the fuel is dry and with enough density. Well designed stoves have been shown to mitigate 1.5 to 3.6 tonnes of carbon dioxide equivalent, thus reducing the impacts on global warming caused by cooking and heating with biomass.
Efficiency: Design differences result in a large variation in efficiency of plancha stoves, with claims ranging from 50% to 80% fuel use reduction. Variations that create the this difference include: internal geometry of the stove that moves the hot gases through the systems; the inclusion or lack of pot rings to provide direct heat transfer into pots; density and thermal characteristics of materials utilized for combustion chambers, the griddle and insulation; diameter and length of the chimney, to name a few. The physical characteristics of the fuel utilized will also create differences in fuel consumption, as well as the ability to remove fuel that has not been consumed from the combustion area vs. leaving it to burn out unnecessarily.
Rocket stoves are defined by improvements to an insulated, L-shaped combustion chamber that allows for partial combustion of gases and smoke inside the stove. As importantly, rocket stoves follow 10 design principles to also improve heat transfer efficiency using insulation and narrow channels directing the flow of hot gases closer to the pot or griddle. This design enables rocket stoves to achieve important emissions benefits as compared to three stone fires or crude stoves. Production of rocket stoves can range from centrally mass-produced products to locally produced artisanal products.
Fuel Type: Raw or processed biomass
Health Impacts: Lab tests to date show a wide variety in the performance of rocket stoves, even in laboratory settings. Some rocket stoves on the market can achieve emissions reductions of roughly 70% or more for carbon monoxide, and over 50% for particulates in a laboratory setting. Studies by USAID, Berkeley Air, and Columbia University found a consistent 40% reduction in fuel use as compared to traditional stoves. The Alliance is supporting field studies on emissions performance of these stoves and expects to find that performance in the field is likely to be highly variable, depending on the stove, the fuel quality, and the individual user.
Climate Impacts: Limited lab testing of rocket stoves to date suggests that some of the insulated mass-produced versions of this stove will reduce net warming impacts by nearly 60%. Rocket stoves may have little to no impact on emissions of black carbon, which is less of a criticism (they were not designed to), than an observation. It is likely that current rocket stoves could be redesigned to offer reductions in black carbon emissions.
Efficiency: Fuel use savings vary widely with the type of rocket stove used. Lab tests show that performance can vary from increasing fuel use for poorly designed, high mass rocket stoves, to fuel savings of up to 50%. Independent field testing of these stoves has found that several leading rocket stoves do in fact achieve substantial (40-50%) reductions in fuel use.
Solar cookstoves, often called solar cookers, can be used in areas where solar energy is abundant for most of the year, which NASA's solar insolation maps indicate is between 30 degrees north and south of the equator, consequently where much of the developing world is located. There are three types of solar cookers: panel, box and parabolic, all of which generate heat by directly capturing the sun's solar thermal energy.
The panel cooker, the least expensive and most portable design, works like an oven. It can heat a cooking pot to temperatures between 250 and 300 F (121-177C). Panel solar cookers use reflective foil bonded to a plastic, metal, wood or cardboard backing which is folded into a clamshell shape to collect sunlight.
Box cookers work on the same principle as a panel cooker. They are bigger and less portable than panel cookers and can be made with cardboard, wood, metal or plastic. Larger models can hold several cooking pots. Solar box cookers reach temperatures between 350 and 400F (177-204C) and like panel cookers present no fire danger.
Parabolic cookers resemble satellite dishes. They cook as fast as an open fire by concentrating sunlight on the bottom of a cooking pot. Parabolic solar cookers can be used from sunup until sundown. They generate temperatures above 450F (232C) even in sub-zero weather.
Fuel Type: Direct solar thermal energy
Health Impacts: Solar cookers produce no smoke and do not contribute to any health impacts associated with cooking.
Climate Impacts: Solar cookers emit no greenhouse gasses and do not contribute to climate change.
Efficiency: While the efficiency of solar stoves depends on the strength of the sun at any given time, the “fuel” is available at no cost, making it a cost-effective solution, especially for populations with limited access to other fuel sources.